The present invention relates to an electrical rotating machine and, more particularly, relates to the electrical rotating machine in which inner rotor and outer rotor are coaxially arranged with a single stator sandwiched therebetween (viz., with a single stator as a center between the inner rotor and outer rotor), each of the inner and outer rotors having a plurality of permanent magnets in a circumferential direction thereof and being driven by means of a compound current supplied to flow through stator coils.
A Japanese Patent Application First Publication No. Heisei 11-356015 published on Dec. 24, 1999 exemplifies a previously proposed rotating machine having a three layer structure described above.
Generally, it is well known that, in a permanent magnet synchronous rotating machine, a rotor is structured to exhibit a reverse saliency (a reverse saliency characteristic) so that a reluctance torque can be utilized and a magnet quantity (which corresponds to the number of pole pairs that the rotor has) can be reduced. The reverse saliency characteristic exhibited on the rotor structure can be achieved by modifying the permanent magnet synchronous rotating machine into a permanent magnet buried type (an interior permanent magnet) rotating machine. Hence, a normally available rotating machine having a single rotor and a single stator generally provides the rotor with the reverse saliency characteristic. It may be considered to be a general practice that, even in the rotating machine having the three-layer structure described in the above-described Japanese Patent Application First Publication, both of the two rotors are, respectively, provided with the reverse saliency characteristics.
However, in the rotating machine having two rotors described in the BACKGROUND OF THE INVENTION, both interlinkage magnetic fluxes of the inner rotor and outer rotor pass through the single stator. Therefore, if both of the two rotors have the reverse saliency characteristics, q-axis interlinkage magnetic fluxes of the inner rotor and the outer rotor pass through the single stator. Therefore, if both rotors have the reverse saliency characteristics, q-axis interlinkage magnetic flux xcexq caused by q-axis inductance Lq is increased so that a stator interlinkage magnetic flux is saturated. Thus, an output (magnetic flux) density cannot be raised. If output (magnetic flux) densities are tried to be increased, an area of the stator becomes large.
It is, therefore, an object of the present invention to provide an electrical rotating machine in which the two rotors are coaxially arranged so that a miniaturization of the stator is made possible, if the quantity of buried magnets (the number of magnets) is the same, and a reduction of the quantity of buried magnets is made possible if the stator structure is left unchanged.
According to one aspect of the present invention, there is provided an electrical rotating machine, comprising: at least two rotors, each of the rotors having a plurality of permanent magnets along its circumferential direction thereof and arranged coaxially with the other rotor and being driven by means of a compound current supplied to stator coils; and a single stator having a plurality of stator coils through which the compound current is caused to flow, one of the rotors exhibiting a forward saliency characteristic and the other rotor exhibiting a reverse saliency characteristic.
According to another aspect of the present invention, there is provided a method applicable to an electrical rotating machine, the electrical machine comprising: at least two rotors, each rotor having a plurality of permanent magnets along its circumferential direction thereof, arranged coaxially with the other rotor, and being driven by means of a compound current supplied to stator coils; and a single stator having a plurality of stator coils through which the compound current is caused to flow, the method comprising: exhibiting a forward saliency characteristic for one of the rotors; and exhibiting a reverse saliency characteristic for the other rotor.
This disclosure of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.